The following conventional techniques for an information processing apparatus using cryptography are known.
In JP-A-275115/1998, there is disclosed a cryptographic technique of encrypting information and storing the encrypted information into an external storage device such as a hard disk drive. In this conventional cryptographic technique, when encrypted data Ya and Yb stored in an external storage device 12 are transferred to an information terminal unit 11, the encrypted data Ya and Yb are decrypted in succession using a deciphering key Kb held in an enciphering/deciphering key custody area 35.
JP-A-214233/1998 discloses another cryptographic technique of providing a dedicated cryptographic processor in an information processing apparatus. According to this conventional cryptographic technique, the cryptographic processor for encrypting data to generate a body of a secure file is equipped in a portable-type personal computer.
In common applications of encryption and decryption processing, sensitive information to be kept in secrecy resides in main memory since data processing is carried out on the main memory. For information encryption in which information is processed through an encryption algorithm, it is required to securely handle the encryption algorithm, cipher key information, and sensitive information to be encrypted.
The above-cited conventional cryptographic techniques, however, give rise to the following problems:
In the conventional cryptographic techniques, since sensitive information and intermediate results of encryption processing are held in main memory, there is a problem that the sensitive information may be extracted by any means. In an information processing apparatus comprising a plurality of semiconductor devices serving as a CPU, main memory and other circuits, when encryption processing is carried out under control of the CPU, an encryption algorithm, sensitive information to be encrypted, and intermediate results of the encryption processing are held in the main memory, causing the above problem of information extractability.
Further, since the information processing apparatus contains signal lines (e.g., bus lines) for interconnecting semiconductor device components thereof, data prior to encryption or decrypted data may be easily extracted by means of tapping the signal line and analyzing data attained through the tapping.
In JP-A-297626/1990, it has been proposed to provide a cryptographic technique of delivering encrypted data to external signal lines. In this conventional cryptographic technique, key information necessary for encryption is supplied from an external source. Therefore, unless security protection of the key information is ensured, there arises a problem that data encryption becomes useless.